1. Field of Invention
This invention relates to improved petroleum cracking catalysts and their method of use.
2. Description of the Previously Published Art
Modern automotive vehicles powered by conventional spark ignition, internal combustion engines are required by law to be equipped with catalytic converters to reduce emissions of hydrocarbons, carbon monoxide and nitrogen oxides in the engine exhaust stream. Formerly, before the introduction of catalytic converters, the octane number of the gasoline obtained by catalytic cracking of petroleum feedstocks was increased by the addition of reformates, alkylates, tetraethyl lead, and/or other octane improving metal and non-metal compounds.
Unfortunately, tetraethyl lead and other metal and non-metal additives for octane boosting or octane improvement of gasoline such as other lead compounds, manganese compounds, boron compounds, phosphorous compounds, etc., deactivate or poison the catalyst in the catalytic converters so that the converter cannot reduce the noxious emissions to acceptable levels. Therefore, such octane improvement compounds cannot be used to increase the octane number of gasoline suitable for vehicles equipped with catalytic converters. Gasolines suitable for vehicles equipped with catalytic converters are commonly termed "unleaded" or "non leaded" gasolines.
The recent increase in the commercial value of hydrocarbons such as reformate, alkylate, etc., which can be added to gasoline to increase its octane number, makes it desirable to sell such valuable chemicals separately as petrochemicals rather than to add them to gasoline to increase the octane number of gasoline.
Thus, both the requirement for unleaded gasolines with a good octane number for vehicles equipped with catalytic converters and the increase in value of reformates, alkylates, etc. for products other than gasoline have prompted the petroleum refining industry to employ novel cracking catalysts which yield a higher octane gasoline than that obtained by conventional cracking catalysts. Cracking catalysts are described in U.S. Pat. Nos. 3,994,800, 4,259,212, 4,324,698, 4,339,354 and 4,325,813 which produce higher octane gasoline than conventional cracking catalysts. They all employ some form of faujasite type Y zeolite.
U.S. Pat. Nos. 3,758,403, 3,894,931, 3,894,933, 4,309,279, and 4,309,280 disclose the use of zeolite Y admixed with zeolite ZSM-5 in the FCC catalyst particle or the use of a mixture of two FCC catalysts, one a conventional cracking catalyst using Y and the other using ZSM-5, or the use of a conventional FCC catalyst with finely powdered ZSM-5 added to the charge stock to make higher octane gasoline. U.S. Pat. No. 4,340,465 discloses the use of a FCC catalyst employing a mixture of Silicalite and rare earth exchanged Y to make a higher octane gasoline.
Zeolite Beta was disclosed in U.S. Pat. No. 3,308,069 and U.S. Pat. No. Re 28,341. Mention is made in U.S. Pat. No. 3,308,069 of the possible use of Beta in a variety of hydrocarbon conversion catalysts including catalytic cracking, columns 7-8, but not in FCC cracking. More specifically, the use of Beta has been described for hydrocracking, U.S. Pat. Nos. 3,923,641 and 4,486,296; for alkylation, U.S. Pat. Nos. 3,957,621, 3,948,758, and 4,301,316; for Diels Alder reaction, U.S. Pat. No. 4,384,153; for dewaxing, UK No. 2,141,733A, and dewaxing on Pt-Beta, U.S. Pat. No. 4,419,220; for isomerization, U.S. Pat. No. 4,518,485 and for conversion of syngas or Fischer Tropsch products into liquid hydrocarbon products, U.S. Pat. Nos. 4,471,145, 4,500,417, 4,543,347 or higher weight hydrocarbons, U.S. Pat. No. 4,476,330. All of these processes involve the use of moderate pressure of hydrogen to be present or involve hydrocarbon synthesis. Also, the use of Beta has been claimed for the conversion of olefins to aromatics, U.S. Pat. No. 4,465,884, and to higher molecular weight low pour point distillates, U.S. Pat. No. 4,430,516. A process has been disclosed for the use of USY, Beta or ZSM-20 exchanged with alkali ions at pH 7 as a component in an FCC catalyst with a high selectivity for distillate, U.S. Pat. No. 4,481,104.